The present invention relates to a data converter and, more particularly, to a data converter for a CRT video display system for converting address information in a first format to a second format.
There are many CRT video display systems in which it is desired to display alphanumeric data characters on a CRT video display monitor. These data characters are typically displayed in successive display rows of a monitor with each data character in a row having a specified row and column display location. The data characters to be displayed in rows of a CRT monitor are generally stored in a binary fashion in succession in a storage device, for example, a random access memory (RAM), and addressed by binary address information in a row/column format.
While the abovementioned data storage technique is quite common and acceptable, if the maximum number of data characters which can be displayed in a display row of a CRT display monitor cannot be represented by an integral power of two, the storage device used to store the binary representations of the data characters to be displayed by the monitor ordinarily must have a storage capacity in excess of the maximum number of character display locations in the display field of the display monitor. By way of example, if a CRT display monitor is arranged to have a standard display field of 25 rows of characters with a maximum of 80 characters per row, for a total of 2000 (80.times.25) character display locations, the storage device required to accommodate this size of display field must have at least 25.times.2.sup.7, or 3200, data character storage locations. The factor 2.sup.7 thus represents the smallest integral power of 2 to accommodate the 80 display locations. Generally, a storage capacity of 3200 data character storage locations can be provided in a storage device in the form of three discrete 1K random access memories, each having 1024 bits or data character storage locations, and a single 128-bit random access memory providing 128 data character storage locations, for a total of 3200 (3072+128) data character storage locations. Since this number of data character storage locations exceeds the size of the display field (2000 display locations) of the display monitor by 1200 locations (3200-2000 ) this excess capacity represents substantial unused capacity, specifically, 2.sup.7 -80, or 48, unused locations per display row. Consequently, unnecessary costs are incurred for storage capacity not actually utilized and, in addition, further costs are incurred due to the added labor required to assemble several discrete memory (RAM) devices into a single memory and also to provide necessary additional power supplies for the several memory devices.